1. Field of the Invention
Embodiments of the invention generally relate to the manufacture of welding wire, and more particularly to a system and method for polishing and lubricating aluminum welding wire.
2. Discussion of Related Art
Aluminum welding wire is often used in continuously fed welding machines. During manufacture, the wire is subjected to various processes including one or more drawing processes that result in a wire having a desired diameter. The drawn wire is then spooled in several layers on a spool or wound into a drum, both of which are for gas metal arc welding or the gas metal arc welding process. When fit up to a continuous welding apparatus, it may be fed off the spool through guides in the feeding means of the continuous welding apparatus. Within such continuous welding apparatus, the wire comes in contact with many parts, including but not limited to, drive rolls, contact tip, guides, and a liner. In order to perform satisfactorily in the welding operation, the aluminum wire must be free from surface contaminants, such as drawing lubricants, so that such contaminants do not contribute to weld defects, such as porosity and the like.
Providing aluminum welding wire that is free of surface contaminants in the form of hydrocarbons (i.e., lubricants) can also be a problem. Lubricant-free wire can result in an undesirable amount of friction during the wire feeding process. Such high degrees of friction can generate wire particulates, which are tiny pieces of material scratched off of the surface of the wire.
In addition, 5xxx-series aluminum alloys have a high level of magnesium. As such, diamond draw dies must be used to fabricate the wire from an original, large, diameter to a smaller diameter. The diamond draw dies scratch the surface of the wire and themselves generate small particulates of aluminum termed fines. These fines can be 1-micron in size or less and are very hard. The fines adhere to the wire's surface, and when the wire is later fed through welding equipment, the fines can dislodge and become embedded in the inner diameter of the liner of the welding equipment. Such build-up can cause additional scratching of the wire's surface. In addition, over time the liner can build up extensive wire shavings that can eventually fully impede the wire's movement through the liner.
This wire shaving problem has never been totally eliminated with clean, lubricant-free wire. Inert lubricants such as carbon/graphite have been used, but such lubricants are particulate materials that adhere to the wire's surface, and although they reduce the tendency for shaving generation, they do not totally eliminate it due to the amount of graphite that is disposed on the surface. That is, only a small portion of the wire's surface will have carbon/graphite particulate on it, so the sensitivity of the lubricant is minor versus having the entire wire's surface coated with a lubricant. Trials have been conducted with other non-hydrocarbon lubricants such as polytetrafluoroethylene (PTFE), commonly known as Teflon. The problem with Teflon, however, is that it is an insulator, and as a result the current needed to melt the wire during the welding operation is non-uniform and so can create arc instability.
Other process changes have been attempted, such as adjusting the wire's temper/hardness, making cast and helix changes, and adjusting wire diameter have been attempted in an effort to eliminate the shaving problem, but none of these attempts have met with success. Thus, there remains a need for an improved process for providing aluminum welding wire for use in continuously fed welding machines that is substantially free of scratches and that also minimizes the chance for generating fines that can reduce the efficiency of such machines.